Immunohistochemical localisation of intravitreally injected bevacizumab in the anterior chamber angle, iris and ciliary body of the primate eye

The progress of assessment methods and treatments of neovascular glaucoma secondary to central retinal vein occlusion

Neovascular glaucoma is a condition that results from central retinal vein occlusion and often leads to blindness. Accurate evaluation and appropriate treatment are crucial for patients. However, there is currently no uniform and clear standard to differentiate between ischemic and non-ischemic central retinal vein occlusion. Also, the assessment of neovascular glaucoma progression is uncertain. Meanwhile, although pan-retinal photocoagulation is a standard treatment to prevent the onset of neovascular glaucoma, its actual efficacy and the timing of intervention remain highly controversial. It is still challenging to balance the risks of side effects in the visual field against the uncertain effectiveness of the treatment. This paper delves into the pathogenesis of neovascular glaucoma to understand the development of therapeutic approaches. By taking into account various assessment criteria of central retinal vein occlusion and neovascular glaucoma over the years, combining functional tests and morphological tests provides the most accurate and rigorous solution. The age of patients, the extent, location, and duration of retinal ischemia are the primary factors that affect the severity and extent of ischemic central retinal vein occlusion and induce serious complications. From the perspective of prevention and treatment, the ischemic index is closely related to the development of neovascularization. The paper provides essential insights into the mechanism, efficacy, complications, and optimal timing of pan-retinal photocoagulation. Comparing the treatment effects of pan-retinal photocoagulation and intravitreal anti-VEGF injections, we suggest a combination of both treatments to explore effective treatment with fewer side effects in the long term. This article details the debate on the above issues and explores ideas for the clinical diagnosis and preventive treatment of neovascular glaucoma that results from ischemic central retinal vein occlusion.

Protein Drug Delivery Using a Novel Maxillofacial Technique Targeting the Visual Pathway in the Brain, the Optic Nerve, and the Retina

Protein drugs are used for treating many diseases of the eye and the brain. The formidable blood neural barriers prevent the delivery of these drugs into the eye and the brain. Hence, there is a need for a protein drug delivery system to deliver large proteins across blood-neural barriers. Low half-life, poor penetration of epithelial barriers, low stability, and immunogenicity limit the use of non-invasive systemic routes for delivering proteins. In this pre-clinical study, the efficacy of a new maxillofacial route for administering protein drugs using a novel drug delivery system is compared with systemic administration through intra-peritoneal injection and ocular administration through topical eye drops and subconjunctival and intravitreal injections. Bevacizumab and retinoschisin proteins were administered using the maxillofacial technique along with systemic and ocular routes in wild-type male C57BL/6J mice. Liquid chromatography with tandem mass spectrometry and western blot was used to detect bevacizumab in tissue samples. Furthermore, immunohistochemistry was performed to detect the presence and localization of bevacizumab and retinoschisin in the retina and brain. The maxillofacial route of delivery could target the brain including regions involved in the visual pathway and optic nerve. The maxillofacial technique and intravitreal injection were effective in delivering the drugs into the retina. A new concept based on the glymphatic pathway, cerebrospinal fluid drug distribution, and the crossover of ipsilateral optic nerve fibers at optic chiasma is proposed to explain the presence of the drug in contralateral eye following maxillofacial administration and intravitreal injection.

Effects of commonly used intravitreal anti-vascular endothelial growth factor drugs on mesenchymal stem cells derived from the limbus and ciliary body

BACKGROUND

To investigate the effects of commonly used intravitreal anti-vascular endothelial growth factor (anti-VEGF) antibodies on proliferation index and viability of mesenchymal stem cells derived from ciliary body and limbus (CB-MSC and LMSC).

METHODS

CB-MSCs and LMSCs were isolated from newborn rats' eyes, and they were expanded in medium by the explant method. Intravitreally used anti-VEGF drugs, aflibercept, bevacizumab and ranibizumab were tested into the 16-well plates, respectively, at four different concentrations. After keeping them for 48 h, the proliferation indexes and viabilities of CB-MSCs and LMSCs were compared separately by Real-Time Cell Analyzer and Methylthiazoltetrazoli (MTT) test.

RESULTS

Anti-VEGFs used at 5-times and 10-times of the standard clinical dosage caused statistically significant negative effects on proliferation indexes of CB-MSCs and LMSCs at the 24^th hour compared to control group. Only the anti-VEGF group that had 10-times dosage of those used clinically had a statistically significant negative effect on the viabilties of CB-MSCs and LMSCs.

CONCLUSION

Administrations of high doses or repeated standard doses of intravitreal anti-VEGF agents may affect the proliferation indexes and viabilities of CB-MSCs and LMSCs adversely. These novel findings deserve further in vivo investigations.

The effects of VEGF-A-inhibitors aflibercept and ranibizumab on the ciliary body and iris of monkeys

PURPOSE

To investigate the effects of intravitreal ranibizumab (Lucentis®) and aflibercept (Eylea®) on the ciliary body and the iris of 12 cynomolgus monkeys with regard to the fenestrations of their blood vessels.

MATERIALS AND METHODS

Structural changes in the ciliary body and in the iris were investigated with light, fluorescent, and transmission electron microscopy (TEM). The latter was used to specifically quantify fenestrations of the endothelium of blood vessels after treatment with aflibercept and ranibizumab. Each of the two ciliary bodies treated with aflibercept and the two treated with ranibizumab and their controls were examined after 1 and 7 days respectively. Ophthalmological investigations including funduscopy and intraocular pressure measurements were also applied.

RESULTS

Ophthalmological investigations did not reveal any changes within the groups. Both drugs reduced the VEGF concentration in the ciliary body pigmented epithelium. The structure of the ciliary body was not influenced, while the posterior pigmented epithelium of the iris showed vacuoles after aflibercept treatment. Ranibizumab was mainly concentrated on the surface layer of the ciliary epithelium, in the blood vessel walls and the lumen of some of the blood vessels, and in the cells of the epithelium of the ciliary body. Aflibercept was more concentrated in the stroma and not in the cells of the epithelium, but as with ranibizumab, also in the blood vessel walls and some of their lumina, and again on the surface layer of the epithelium. Both aflibercept-and ranibizumab-treated eyes showed a decreased number of fenestrations of the capillaries in the ciliary body compared to the untreated controls. On day 1 and day 7, aflibercept had fewer fenestrations than the ranibizumab samples of the same day.

CONCLUSIONS

Both aflibercept and ranibizumab were found to reach the blood vessel walls of the ciliary body, and effectively reduced their fenestrations. Aflibercept might eliminate VEGF to a greater extent, possibly due to a higher elimination of fenestrations in a shorter time. Moreover, the vacuoles found in the iris need further research, in order to evaluate whether they carry a possible pathological potential.

Pharmacokinetics and distributions of bevacizumab by intravitreal injection of bevacizumab-PLGA microspheres in rabbits

AIM

To investigate the pharmacokinetics and distributions of bevacizumab by intravitreal injection of prepared bevacizumab-poly (L-lactic-co-glycolic acid) (PLGA) microspheres in rabbits, to provide evidence for clinical application of this kind of bevacizumab sustained release dosage form.

METHODS

Bevacizumab was encapsulated into PLGA microsphere via the solid-in-oil-in-hydrophilic oil (S/O/hO) method. Fifteen healthy New Zealand albino-rabbits were used in experiments. The eyes of each rabbit received an intravitreal injection. The left eyes were injected with prepared bevacizumab-PLGA microspheres and the right eyes were injected with bevacizumab solution. After intravitreal injection, rabbits were randomly selected at days 3, 7, 14, 28 and 42 respectively, three animals each day. Then we used immunofluorescence staining to observe the distribution and duration of bevacizumab in rabbit eye tissues, and used the sandwich ELISA to quantify the concentration of free bevacizumab from the rabbit aqueous humor and vitreous after intravitreal injection.

RESULTS

The results show that the concentration of bevacizumab in vitreous and aqueous humor after administration of PLGA formulation was higher than that of bevacizumab solution. The T1/2 of intravitreal injection of bevacizumab-PLGA microspheres is 9.6d in vitreous and 10.2d in aqueous humor, and the T1/2 of intravitreal injection of soluble bevacizumab is 3.91d in vitreous and 4.1d in aqueous humor. There were statistical significant difference for comparison the results of the bevacizumab in vitreous and aqueous humor between the left and right eyes (P<0.05). The AUC0-t of the sustained release dosage form was 1-fold higher than that of the soluble form. The relative bioavailability was raised significantly. The immunofluorescence staining of PLGA-encapsulated bevacizumab (b-PLGA) in rabbit eye tissues was still observed up to 42d. It was longer than that of the soluble form.

CONCLUSION

The result of this study shows the beneficial effects of PLGA in prolonging the residency of bevacizumab in the vitreous. And the drug delivery system may have potential as a treatment modality for related disease.

[Ocular hypertension after intravitreal steroid injections: Clinical update as of 2015]

Intravitreal injections are a therapeutic delivery method best suited to the treatment of retinal diseases. Recent years have been marked by the use of anti-VEGF agents as well as the arrival of sustained-release corticosteroid implants in France, replacing triamcinolone acetonide. A common complication of IVT steroids is secondary ocular hypertension (OHT) resulting from increased outflow resistance. This article summarizes current understanding. OHT induced by topical steroids has been described for 60 years. Intravitreal use also shows a temporary effect if the exposure is short, dose dependence, and varying incidence depending on the drug used. Sustained release formulations and discontinuing treatment have reduced the risk of induced OHT. Risk factors that induce OHT must be clearly identified prior to an injection. Most cases of OHT can be controlled medically, although differences exist between different drugs. In cases where it cannot be controlled, removal of the implant, selective laser trabeculoplasty, and filtration surgery can be discussed.

Current and investigational pharmacotherapeutic approaches for modulating retinal angiogenesis

Retinal vascular development is a carefully orchestrated developmental process during which retinal and choroidal vasculature form to provide a dual vascular supply to the neurosensory retina and retinal pigment epithelium. The most common causes of vision loss in children and adults involve at least in part perturbation of the normal vascular physiology or development. Vascular endothelial growth factor has emerged as a key molecular regulator of retinal vascular development as well as retinal and choroidal neovascularization, which underlie the pathophysiology of many retinal diseases. Over the past decade, the advent of injectable pharmacotherapeutic agents into the vitreous cavity of the eye has revolutionized our management of neovascular age-related macular degeneration and other retinal diseases and has, for the first time, offered an opportunity to improve vision rather than just slow the progression of disease processes. The transient duration of these agents, however, requires chronic treatment with repeated intraocular injections and significant treatment burden for patients and the healthcare system. Novel treatments modulating retinal angiogenesis offer the promise of improved efficacy, decreased treatment burden and improved cost-effectiveness.

Expression and role of VEGF--a in the ciliary body

PURPOSE

The role of VEGF-A in the normal ciliary body is largely unexplored. The ciliary body is similar in many respects to the choroid plexus of the brain, and we demonstrated previously the importance of VEGF-A in maintenance of choroid plexus vasculature and ependymal cells. Therefore, the role of VEGF-A in ciliary body homeostasis was explored.

METHODS

Swiss-Webster mice (VEGF-LacZ) were used to determine VEGF-A expression during ciliary body development and in the adult. VEGFR2 expression was determined in adult wild type C56BL/6J mice. Systemic VEGF-A neutralization in vivo was achieved with adenovirus-mediated overexpression of soluble VEGFR1 (sFlt1). Following VEGF-A neutralization, the ciliary epithelium was analyzed by light microscopy and transmission electron microscopy (TEM). The effect of VEGF-A blockade on ciliary body function also was assessed by measuring intraocular pressure.

RESULTS

VEGF-A expression was detected at embryonic day 18.5 (E18.5), the onset of ciliary process formation. In the adult ciliary body, VEGF-A was expressed by the pigmented epithelium, whereas VEGFR2 was localized primarily to the capillary endothelium and nonpigmented epithelium. Systemic VEGF-A neutralization led to a thinning of the nonpigmented epithelium, vacuolization of the pigmented epithelium, loss of capillary fenestrations, and thrombosis. These changes were associated with impaired ciliary body function, as evidenced by decreased intraocular pressure in sFlt1-overexpressing animals (15.31 ± 2.06 mm Hg) relative to controls (18.69 ± 1.49 mm Hg).

CONCLUSIONS

VEGF-A has an important role in ciliary body homeostasis. Potential for undesired off-target effects should be considered with the chronic use of anti-VEGF-A therapies.

Anti-VEGF Agents for Ocular Angiogenesis and Vascular Permeability

We review articles describing intravitreal injection of anti-VEGF drug trials, while discussing the mechanisms of the action of anti-VEGF antibodies, and also evaluating their outcomes. Intraocular injections of anti-VEGF drug are considered to be an effective treatment for macular edema after retinal vein occlusion, however, recurrent/persistent edema is common. The recent reports may lead to a shift in treatment paradigm for DME, from laser photocoagulation, to newer approaches using anti-VEGF drugs. There have been several well-publicized prospective, randomized studies that demonstrated the efficacy of intravitreal injection of anti-VEGF drugs for patients with AMD. Adjuvant bevacizumab for neovascular glaucoma may prevent further PAS formation, and it is likely to open up a therapeutic window for a panretinal photocoagulation and trabeculectomy. Intravitreal injection of bevacizumab (IVB) results in a substantial decrease in bleeding from the retinal vessels or new vessels during a standard vitrectomy. IVB has also been reported to be effective for inducing the regression of new vessels in proliferative diabetic retinopathy. The use of bevacizumab in stage 4 or 5 retinopahty of permaturity (ROP) is to reduce the plus sign to help reduce hemorrhage during the subsequent vitrectomy. Some authors reported cases of resolution of stage 4 A ROP after bevacizumab injection.

Posterior vitreous detachment with microplasmin alters the retinal penetration of intravitreal bevacizumab (Avastin) in rabbit eyes

PURPOSE

Intravitreal bevacizumab (BV) (Avastin, Genentech Inc., South San Francisco, CA) is frequently used for the treatment of age-related macular degeneration. Previous studies have demonstrated full-thickness retinal penetration. Intravitreal recombinant microplasmin (MP) has been shown to successfully induce a posterior vitreous detachment (PVD) and vitreous liquefaction in animals. It has been suggested that a PVD may alter the retinal penetration of molecules in the vitreous cavity. The aim of this study was to compare BV retinal penetration in rabbit eyes with and without an MP-induced PVD.

METHODS

Twelve adult rabbits were injected with 0.1 mL (0.4 mg) of MP into the vitreous cavity of 1 eye. One week later, the rabbits were injected with 0.05 mL (1.25 mg) of BV into both eyes. Both eyes of 3 rabbits were harvested at 6 hours, 12 hours, 24 hours, and 72 hours after the BV injection. Frozen retinal cross sections were prepared, and BV retinal penetration was evaluated with immunohistochemistry using a fluorescence-labeled antibody against BV. Two eyes from one rabbit were not injected with either agent and used as controls to compare the background autofluorescence. Peripapillary retinal sections were recorded with a digital camera, and intraretinal BV fluorescence-labeled antibody was measured by qualitative photographic interpretation. Two additional rabbits received an intravitreal injection of 0.1 mL of MP in 1 eye. One week later, both eyes from each rabbit were enucleated, and frozen retinal sections were prepared and analyzed with light microscopy to evaluate histologic damage.

RESULTS

Full-thickness BV retinal penetration was observed throughout the retina in both eyes of each rabbit. All the MP-injected eyes exhibited increased antibody labeling in retinas evaluated at 6 hours, 12 hours, and 24 hours after BV injection when compared with the contralateral non-MP-injected eyes. By 3 days after BV injection, all eyes demonstrated decreased antibody labeling compared with earlier periods. At 3 days, 1 rabbit showed increased antibody labeling in the retina of the non-MP-injected eye compared with the contralateral MP-injected eye, and 2 rabbits exhibited similar antibody labeling in both eyes. When compared with control eyes, light microscopy demonstrated normal retinal histologic findings in eyes injected only with MP.

CONCLUSION

Increased BV retinal penetration is observed initially in eyes with an MP-induced PVD, and the mechanism is likely multifactorial. By 3 days, retinal penetration is similar in eyes with and without a PVD. Although it is difficult to directly extrapolate to humans, our study suggests that a PVD may alter the retinal penetration of BV.

Injection site and pharmacokinetics after intravitreal injection of immunoglobulin G

PURPOSE

The aim of this study was to investigate whether the pharmacokinetics differ after immunoglobulin G (IgG) intravitreal injections are done in the different sites of the vitreous cavity of rabbit eyes.

METHODS

To examine the pharmacokinetics in the vitreous and the retina/choroid, fluorescein isothiocyanate-labeled IgG (5  μg/50  μL) was injected from the superior pars plana into the vitreous cavity of rabbit eyes. An original intravitreal injection guide was used to fix the tip of the injection needle, with the tip fixed in either the superior-anterior vitreous (superior group) or in the posterior vitreous (posterior group). At 1  h, 1, 4, and 7 days after injection, the eyes were enucleated and frozen. The vitreous was cut into superior, inferior, and posterior vitreous sections, whereas the retina/choroid was cut into superior, inferior, and posterior retina/choroid sections. The IgG concentrations in the vitreous and the retina/choroid sections were then determined.

RESULTS

In the posterior vitreous, the IgG concentration in the posterior group was significantly higher than that in the superior group at 1  h after injection (P < 0.05). However, 1 day after injection, no significant differences were noted between the 2 groups. At 4 days after injection, the drug was diffusely spread in both groups. In the posterior retina/choroid, the IgG concentration was essentially the same regardless of the injection site or the amount of time after injection. The IgG concentration in the superior retina/choroid was significantly higher in the superior group than in the posterior group at 1  h and 1 day after injection (P < 0.05). There were no differences noted between the 2 groups for the IgG concentrations in the 3 sections at 4 and 7 days after injection.

CONCLUSIONS

Intravitreally injected IgG remains in the area of the injection, with more than 1 day required for it to spread diffusely within the vitreous. In the posterior retina/choroid, results suggested that the concentration of IgG may be equal regardless of the injection site. In the superior retina/choroid area that was near the site of the injection, the concentration of drug tended to be higher.